1. Field of the Invention
The present invention pertains to methods and apparatus for forming, filling and sealing bags or packages with various materials. Specifically, it pertains to methods and apparatus for forming, filling and sealing bags or packages with fluid materials.
2. Description of the Prior Art
One of the most modern types of processing machinery for filling bags, packages, pouches, etc, with dry particulate products or with liquid products is a machine referred to as the vertical form-fill-seal machine. With these machines, a flat continuous roll of bagging material may be formed into a tube, sealed at the bottom, filled and then sealed at the top. Examples of such machines may be seen in U.S. Pat. Nos. 3,826,061; 3,849,965; 4,077,308 and 4,090,344.
In such a vertical form-fill-seal (VFFS) machine, a flat sheet of packaging material is first formed into a tube or hose by automatically shaping the bagging material into a tube or hose, bringing the edges of the sheet together and longitudinally sealing the bagging material at this juncture. A pair of sealing jaws are provided in the machine which are transversely movable toward each other to engage the bagging material, after it is in the shape of a hose or tube, to form a transverse seal providing the top closure for a lower bag and a bottom closure for a succeeding upper bag. The material to be placed in the bag is measured and introduced into the upper or succeeding bag and the bagging material advanced by the sealing jaws or some other mechanism, and the sealing jaws are released from its sealing position, repositioned and moved toward each other to again engage the bagging material, forming a transverse seal providing the top closure of the filled bag and the bottom closure of still another succeeding bag.
VFFS machines have long been used to package dry products in both small sizes and large bags, e.g. five and ten pound bags. However, VFFS machines have not been used to package liquids in sizes larger than one liter or one quart. There is a significant problem inherent in attempting to package liquids as opposed to packaging dry products.
Since the upper and lower ends of the bags are flat when they are sealed together, it is necessary that the tube or hose from which they are formed be flat before or as the sealing jaws are brought together. Dry products help hold the bagging material flat since friction between particles restricts the flow of the product. In addition, mechanical means may also be used. Such mechanical means include flattening tubes, spreader wires and deflater pads.
Since liquids flow to equalize pressure, a tube or hose of bagging material filled with liquid tends to assume a rounded cross-section. When the tube of bagging material is flattened for sealing, the force of the liquid resisting flattening increases to resist such flattening. As the sealing jaws close on the tube of bagging material as it hangs filled with liquid, and there is no control over how the tube moves as it becomes flat, there is very likely to be wrinkles in the seal areas. This will likely produce leaking bags resulting in the loss of the liquid product and creating other problems even in the bags which are sealed.
Various means have been developed to overcome the problems inherent in sealing of bags filled with liquids. For example, in U.S. Pat. No. 3,849,965, a pair of wedges are provided below the sealing jaws of a machine which serve to change the volume of a chamber formed by lateral plates placed on both sides of the hose or tube of bagging material. These wedges also appear to provide a mechanical means of aiding in flattening of the hose or tube of bagging material as it is being sealed by the sealing jaws. However, it appears that such an arrangement would not completely eliminate the wrinkling in the seal area associated with filling bags with liquid, particularly larger size bags. Thus, while the VFFS machine has been widely used for filling bags with dry products, wrinkling in the seal area associated with filling bags with liquid materials has prevented widespread use of the VFFS machine in such applications.